Mapping the Human Chondroitin Sulfate Glycoproteome Reveals an Unexpected Correlation Between Glycan Sulfation and Attachment Site Characteristics

Chondroitin sulfate proteoglycans (CSPGs) control key events in human health and disease and are composed of chondroitin sulfate (CS) polysaccharide(s) attached to different core proteins. Detailed information on the biological effects of site-specific CS structures is scarce as the polysaccharides are typically released from their core proteins prior to analysis. Here we present a novel glycoproteomic approach for site-specific sequencing of CS modifications from human urine. Software-assisted and manual analysis revealed that certain core proteins carried CS with abundant sulfate modifications, while others carried CS with lower levels of sulfation. Inspection of the amino acid sequences surrounding the attachment sites indicated that the acidity of the attachment site motifs increased the levels of CS sulfation, and statistical analysis confirmed this relationship. However, not only the acidity but also the sequence and characteristics of specific amino acids in the proximity of the serine glycosylation site correlated with the degree of sulfation. These results demonstrate attachment site-specific characteristics of CS polysaccharides of CSPGs in human urine and indicate that this novel method may assist in elucidating the biosynthesis and functional roles of CSPGs in cellular physiology.

Dermatopontin in Skeletal Muscle Extracellular Matrix Regulates Myogenesis

Dermatopontin (DPT) is an extensively distributed non-collagenous component of the extracellular matrix predominantly found in the dermis of the skin, and consequently expressed in several tissues. In this study, we explored the role of DPT in myogenesis and perceived that it enhances the cell adhesion, reduces the cell proliferation and promotes the myoblast differentiation in C2C12 cells. Our results reveal an inhibitory effect with fibronectin (FN) in myoblast differentiation. We also observed that DPT and fibromodulin (FMOD) regulate positively to each other and promote myogenic differentiation. We further predicted the 3D structure of DPT, which is as yet unknown, and validated it using state-of-the-art in silico tools. Furthermore, we explored the in-silico protein-protein interaction between DPT-FMOD, DPT-FN, and FMOD-FN, and perceived that the interaction between FMOD-FN is more robust than DPT-FMOD and DPT-FN. Taken together, our findings have determined the role of DPT at different stages of the myogenic process.

Study on the pathological and biomedical characteristics of spinal cord injury by confocal Raman microspectral imaging

Confocal Raman microspectral imaging (CRMI) in combination with multivariate analysis was used to study pathological progression after spinal cord injury (SCI). By establishing moderate contusion in rat models, ex vivo longitudinal spinal cord tissue sections were prepared for microspectroscopic analysis. Comparative studies were then performed to determine the pathological distinctions among before injury (BI), one day post-injury (1 DPI), seven days post-injury (7 DPI), and 14 days post-injury (14 DPI) groups. Multivariate analysis algorithms, including K-mean cluster analysis (KCA) and principal component analysis (PCA), were conducted to highlight biochemical and structural variations after tissue damage. It is confirmed that typical spectral features and profiles can illustrate some fundamental and significant pathological processes post-injury, such as neuron apoptosis, hemorrhage, demyelination, and chondroitin sulfate proteoglycans (CSPGs) upregulation. Further, by establishing spectra-structure correlations, the reconstructed spectral images revealed some minute and important morphological characteristics following tissue injury, such as glial scar formation surrounding the cavity structure. The observed spectral phenomena also provide a detailed view on relevant pathobiological factors, which are involved in the spread of secondary damage after traumatic spinal cord injury. Our findings not only provide a spectral perspective to the well-known cellular mechanisms underlying SCI, but further provide a sound basis for developing real-time Raman methodologies to evaluate the prognostic factors and therapeutic results of SCI.

Molecular Basis for Cohesin Acetylation by Establishment of Sister Chromatid Cohesion N-Acetyltransferase ESCO1

Protein acetylation is a prevalent posttranslational modification that is regulated by diverse acetyltransferase enzymes. Although histone acetyltransferases (HATs) have been well characterized both structurally and mechanistically, far less is known about non-histone acetyltransferase enzymes. The human ESCO1 and ESCO2 paralogs acetylate the cohesin complex subunit SMC3 to regulate the separation of sister chromatids during mitosis and meiosis. Missense mutations within the acetyltransferase domain of these proteins correlate with diseases, including endometrial cancers and Roberts syndrome. Despite their biological importance, the mechanisms underlying acetylation by the ESCO proteins are not understood. Here, we report the X-ray crystal structure of the highly conserved zinc finger-acetyltransferase moiety of ESCO1 with accompanying structure-based mutagenesis and biochemical characterization. We find that the ESCO1 acetyltransferase core is structurally homologous to the Gcn5 HAT, but contains unique additional features including a zinc finger and an ∼40-residue loop region that appear to play roles in protein stability and SMC3 substrate binding. We identify key residues that play roles in substrate binding and catalysis, and rationalize the functional consequences of disease-associated mutations. Together, these studies reveal the molecular basis for SMC3 acetylation by ESCO1 and have broader implications for understanding the structure/function of non-histone acetyltransferases.

Identification of a region in the coiled-coil domain of Smc3 that is essential for cohesin activity

The cohesin complex plays an important role in sister chromatin cohesion. Cohesin's core is composed of two structural maintenance of chromosome (SMC) proteins, called Smc1 and Smc3. SMC proteins are built from a globular hinge domain, a rod-shaped domain composed of long anti-parallel coiled-coil (CC), and a second globular adenosine triphosphatase domain called the head. The functions of both head and hinge domains have been studied extensively, yet the function of the CC region remains elusive. We identified a mutation in the CC of smc3 (L217P) that disrupts the function of the protein. Cells carrying the smc3-L217P allele have a strong cohesion defect and complexes containing smc3-L217P are not loaded onto the chromosomes. However, the mutation does not affect inter-protein interactions in either the core complex or with the Scc2 loader. We show by molecular dynamics and biochemistry that wild-type Smc3 can adopt distinct conformations, and that adenosine triphosphate (ATP) induces the conformational change. The L217P mutation restricts the ability of the mutated protein to switch between the conformations. We suggest that the function of the CC is to transfer ATP binding/hydrolysis signals between the head and the hinge domains. The results provide a new insight into the mechanism of cohesin activity.

Capture and On-chip analysis of Melanoma Cells Using Tunable Surface Shear forces

With new systemic therapies becoming available for metastatic melanoma such as BRAF and PD-1 inhibitors, there is an increasing demand for methods to assist with treatment selection and response monitoring. Quantification and characterisation of circulating melanoma cells (CMCs) has been regarded as an excellent non-invasive candidate but a sensitive and efficient tool to do these is lacking. Herein we demonstrate a microfluidic approach for melanoma cell capture and subsequent on-chip evaluation of BRAF mutation status. Our approach utilizes a recently discovered alternating current electrohydrodynamic (AC-EHD)-induced surface shear forces, referred to as nanoshearing. A key feature of nanoshearing is the ability to agitate fluid to encourage contact with surface-bound antibody for the cell capture whilst removing nonspecific cells from the surface. By adjusting the AC-EHD force to match the binding affinity of antibodies against the melanoma-associated chondroitin sulphate proteoglycan (MCSP), a commonly expressed melanoma antigen, this platform achieved an average recovery of 84.7% from biological samples. Subsequent staining with anti-BRAF(V600E) specific antibody enabled on-chip evaluation of BRAF(V600E) mutation status in melanoma cells. We believe that the ability of nanoshearing-based capture to enumerate melanoma cells and subsequent on-chip characterisation has the potential as a rapid screening tool while making treatment decisions.

Self-Assembly and Collagen-Stimulating Activity of a Peptide Amphiphile Incorporating a Peptide Sequence from Lumican

The self-assembly and bioactivity of a peptide amphiphile (PA) incorporating a 13-residue sequence derived from the last 13 amino acids of the C-terminus of lumican, C16-YEALRVANEVTLN, attached to a hexadecyl (C16) lipid chain have been examined. Lumican is a proteoglycan found in many types of tissue and is involved in collagen fibril organization. A critical aggregation concentration (cac) for the PA was determined through pyrene fluorescence measurements. The structure of the aggregates was imaged using electron microscopy, and twisted and curved nanotapes were observed. In situ small-angle X-ray scattering and fiber X-ray diffraction reveal that these tapes contain interdigitated bilayers of the PA molecules. FTIR and circular dichroism spectroscopy and fiber X-ray diffraction indicate that the lumican sequence in the PA adopts a β-sheet secondary structure. Cell assays using human dermal fibroblasts show that below the cac the PA displays good biocompatibility and also stimulates collagen production over a period of 3 weeks, exceeding a 2-fold enhancement for several concentrations. Thus, this PA has promise in future biological applications, in particular, in tissue engineering.

Cell substrate patterning with glycosaminoglycans to study their biological roles in the central nervous system

Microcontact printing (μCP) based techniques have been developed for creating cell culture substrates with discrete placement of CNS-expressed molecules. These substrates can be used to study various components of the complex molecular environment in the central nervous system (CNS) and related cellular responses. Macromolecules such as glycosaminoglycans (GAGs), proteoglycans (PGs), or proteins are amenable to printing. Detailed protocols for both adsorption based as well as covalent reaction printing of cell culture substrates are provided. By utilizing a modified light microscope, precise placement of two or more types of macromolecules by sequential μCP can be used to create desired spatial arrangements containing multicomponent PG, GAG, and protein surface patterns for studying CNS cell behavior. Examples of GAG stripe assays for neuronal pathfinding and directed outgrowth, and dot gradients of PG + laminin for astrocyte migration studies are provided.

[Cohesion inside eu- and heterochromatin in human cells]

It is considered that sister chromatids are held together immediately after replication by special protein complex--cohesin that consists of Smc1--Smc3 core dimer and two additional subunits, Scc1 and Scc3. This process is called cohesion. We have characterized binding of cohesin complex to early- and late-replicated chromatin at different stages of the cell cycle in human cells HeLa and HT1080 using superresolution microscopy (based on Structural ilumination microscopy--SIM) and immunoelectron microscopy. It has been shown that cohesins do not play important role in cohesion of heterochromatic domains, but they provide cohesion and organization of subdomains in euchromatic regions.

Characterization of a DNA exit gate in the human cohesin ring

Chromosome segregation depends on sister chromatid cohesion mediated by cohesin. The cohesin subunits Smc1, Smc3, and Scc1 form tripartite rings that are thought to open at distinct sites to allow entry and exit of DNA. However, direct evidence for the existence of open forms of cohesin is lacking. We found that cohesin's proposed DNA exit gate is formed by interactions between Scc1 and the coiled-coil region of Smc3. Mutation of this interface abolished cohesin's ability to stably associate with chromatin and to mediate cohesion. Electron microscopy revealed that weakening of the Smc3-Scc1 interface resulted in opening of cohesin rings, as did proteolytic cleavage of Scc1. These open forms may resemble intermediate states of cohesin normally generated by the release factor Wapl and the protease separase, respectively.

Proteoglycans and glycosaminoglycans improve toughness of biocompatible double network hydrogels

Based on the molecular stent concept, a series of tough double-network hydrogels (St-DN gels) made from the components of proteoglycan aggregates - chondroitin sulfate proteoglycans (1), chondroitin sulfate (2), and sodium hyaluronate (3) - are successfully developed in combination with a neutral biocompatible polymer. This work demonstrates a promising method to create biopolymer-based tough hydrogels for biomedical applications.

HDAC8 mutations in Cornelia de Lange syndrome affect the cohesin acetylation cycle

Cornelia de Lange syndrome (CdLS) is a dominantly inherited congenital malformation disorder, caused by mutations in the cohesin-loading protein NIPBL for nearly 60% of individuals with classical CdLS, and by mutations in the core cohesin components SMC1A (~5%) and SMC3 (<1%) for a smaller fraction of probands. In humans, the multisubunit complex cohesin is made up of SMC1, SMC3, RAD21 and a STAG protein. These form a ring structure that is proposed to encircle sister chromatids to mediate sister chromatid cohesion and also has key roles in gene regulation. SMC3 is acetylated during S-phase to establish cohesiveness of chromatin-loaded cohesin, and in yeast, the class I histone deacetylase Hos1 deacetylates SMC3 during anaphase. Here we identify HDAC8 as the vertebrate SMC3 deacetylase, as well as loss-of-function HDAC8 mutations in six CdLS probands. Loss of HDAC8 activity results in increased SMC3 acetylation and inefficient dissolution of the ‘used’ cohesin complex released from chromatin in both prophase and anaphase. SMC3 with retained acetylation is loaded onto chromatin, and chromatin immunoprecipitation sequencing analysis demonstrates decreased occupancy of cohesin localization sites that results in a consistent pattern of altered transcription seen in CdLS cell lines with either NIPBL or HDAC8 mutations.

Versican/PG-M is essential for ventricular septal formation subsequent to cardiac atrioventricular cushion development

Versican (Vcan)/proteoglycan (PG)-M is a large chondroitin sulfate proteoglycan which forms a proteoglycan/hyaluronan (HA) aggregate in the extracellular matrix (ECM). We tried to generate the Vcan knockout mice by a conventional method, which resulted in mutant mice Vcan(Δ3/Δ3) whose Vcan lacks the A subdomain of the G1 domain. The Vcan knockout embryos died during the early development stage due to heart defects, but some Vcan(Δ3/Δ3) embryos survived through to the neonatal period. The hearts in Vcan(Δ3/Δ3) newborn mice showed normal cardiac looping, but had ventricular septal defects. Their atrioventricular canal (AVC) cushion was much smaller than those of wild-type (WT) embryos, and the extracellular space for cardiac jelly was narrow. The Vcan deposition in the Vcan(Δ3/Δ3) AVC cushion had decreased, whereas the HA deposition was maintained and condensed. In the tip of ventricular septa, both Vcan and HA had decreased. The cell proliferation based on the number of Ki67-positive cells had remarkably increased in both the AVC cushion and ventricular septa, compared with that of WT embryos. Vcan(Δ3/Δ3) seemed to have endocardial and mesenchymal mixed characteristics. When the ex vivo explant culture of these regions was performed on the collagen gel, hardly any migration to make sufficient space for the ECM construction was apparent. Our results suggest that the proteoglycan aggregates are necessary in both the AVC cushion and ventricular septa to fuse interventricular septa, and the Vcan A subdomain plays an essential role for the interventricular septal formation by constituting the proteoglycan aggregates.

Type of carbohydrate in feed affects the expression of small leucine-rich proteoglycans (SLRPs), glycosaminoglycans (GAGs) and interleukins in skeletal muscle of Atlantic cod (Gadus morhua L.)

Aquaculture requires feed that ensures rapid growth and healthy fish. Higher inclusion of plant ingredients is desirable, as marine resources are limited. In this study we investigated the effects of higher starch inclusion in feed on muscular extracellular matrix and interleukin expression in farmed cod. Starch was replaced by complex fibers in the low-starch diet to keep total carbohydrate inclusion similar. Blood glucose and fructosamine levels were elevated in the high-starch group. The group fed a high-starch diet showed up-regulation on mRNA level of proteoglycans biglycan and decorin. ELISA confirmed the real-time PCR results on protein level for biglycan and also showed increase of lumican. For decorin the protein levels were decreased in the high-starch group, in contrast to real-time PCR results. Disaccharide analyses using HPLC showed reduction of glycosaminoglycans. Further, there was up-regulation of interleukin-1β and -10 on mRNA level in muscle. This study shows that the muscular extracellular matrix composition is affected by diet, and that a high-starch diet results in increased expression of pro-inflammatory genes similar to diabetes in humans.

Chondroitin sulphate proteoglycans: extracellular matrix proteins that regulate immunity of the central nervous system

The extracellular matrix (ECM) is a complex network of scaffolding molecules that also plays an important role in cell signalling, migration and tissue structure. In the central nervous system (CNS), the ECM is integral to the efficient development/guidance and survival of neurons and axons. However, changes in distribution of the ECM in the CNS may significantly enhance pathology in CNS disease or following injury. One group of ECM proteins that is important for CNS homeostasis is the chondroitin sulphate proteoglycans (CSPGs). Up-regulation of these molecules has been demonstrated to be both desirable and detrimental following CNS injury. Taking cues from arthritis, where there is a strong anti-CSPG immune response, there is evidence that suggests that CSPGs may influence immunity during CNS pathological conditions. This review focuses on the role of CSPGs in CNS pathologies as well as in immunity, both from a viewpoint of how they may inhibit repair and exacerbate damage in the CNS, and how they are involved in activation and function of peripheral immune cells, particularly in multiple sclerosis. Lastly, we address how CSPGs may be manipulated to improve disease outcomes.

Electron tomography reveals multiple self-association of chondroitin sulphate/dermatan sulphate proteoglycans in Chst5-null mouse corneas

The spatial distribution of collagen fibrils in the corneal stroma is essential for corneal transparency and is primarily regulated by extrafibrillar proteoglycans, which are multi-functional polymers that interact with hybrid type I/V collagen fibrils. In order to understand more about proteoglycan organisation and collagen associations in the cornea, three-dimensional electron microscopy reconstructions of collagen-proteoglycan interactions in the anterior, mid and posterior stroma from a Chst5 knockout mouse, which lacks a keratan sulphate sulphotransferase, were obtained. Both longitudinal and transverse section show sinuous, oversized proteoglycans with near-periodic, orthogonal off-shoots. In many cases, these proteoglycans traverse over 400nm of interfibrillar space interconnecting over 10 collagen fibrils. The reconstructions suggest that multiple chondroitin sulphate/dermatan sulphate proteoglycans have aggregated laterally and, possibly, end-to-end, with orthogonal extensions protruding from the main electron-dense stained filament. We suggest possible mechanisms as to how sulphation differences may lead to this increase in aggregation of proteoglycans in the Chst5-null mouse corneal stroma and how this relates to proteoglycan packing in healthy corneas.

Epitope distance to the target cell membrane and antigen size determine the potency of T cell-mediated lysis by BiTE antibodies specific for a large melanoma surface antigen

Melanoma chondroitin sulfate proteoglycan (MCSP; also called CSPG4, NG2, HMW-MAA, MSK16, MCSPG, MEL-CSPG, or gp240) is a surface antigen frequently expressed on human melanoma cells, which is involved in cell adhesion, invasion and spreading, angiogenesis, complement inhibition, and signaling. MCSP has therefore been frequently selected as target antigen for development of antibody- and vaccine-based therapeutic approaches. We have here used a large panel of monoclonal antibodies against human MCSP for generation of single-chain MCSP/CD3-bispecific antibodies of the BiTE (for bispecific T cell engager) class. Despite similar binding affinity to MCSP, respective BiTE antibodies greatly differed in their potency of redirected lysis of CHO cells stably transfected with full-length human MCSP, or with various MCSP deletion mutants and fusion proteins. BiTE antibodies binding to the membrane proximal domain D3 of MCSP were more potent than those binding to more distal domains. This epitope distance effect was corroborated with EpCAM/CD3-bispecific BiTE antibody MT110 by testing various fusion proteins between MCSP and EpCAM as surface antigens. CHO cells expressing small surface target antigens were generally better lysed than those expressing larger target antigens, indicating that antigen size was also an important determinant for the potency of BiTE antibody. The present study for the first time relates the positioning of binding domains and size of surface antigens to the potency of target cell lysis by BiTE-redirected cytotoxic T cells. In case of the MCSP antigen, this provides the basis for selection of a maximally potent BiTE antibody candidate for development of a novel melanoma therapy.

Distinct targets of the Eco1 acetyltransferase modulate cohesion in S phase and in response to DNA damage

Chromosome segregation and the repair of DNA double-strand breaks (DSBs) require cohesin, the protein complex that mediates sister chromatid cohesion. Cohesion requires both a chromatin binding step and a subsequent tethering step called cohesion generation. Here we provide insight into how cohesion generation is restricted to S phase but can be activated in G2/M by a DSB in budding yeast. We show that Wpl1p inhibits cohesion in G2/M. A DSB counteracts Wpl1p and stimulates cohesion generation by first inducing the phosphorylation of the Mcd1p subunit of cohesin. This phosphorylation activates Eco1p-dependent acetylation of Mcd1p, which in turn antagonizes Wpl1p. Previous studies show that Eco1p antagonizes Wpl1p in S phase by acetylating the Smc3p subunit of cohesin. We show that Mcd1p and Smc3p acetylation antagonize Wpl1p only in their proper context. Thus, Eco1p antagonizes Wpl1p in distinct ways to modulate cohesion generation during the cell cycle and after DNA damage.

[Axonal growth inhibition by chondroitin sulfate proteoglycans in the central nervous system]

Chondroitin sulphate proteoglycans (CSPG) are components of the extracellular matrix, consisting of peptides chemically attached covalently to chains of glycosaminoglycans. There are 4 families of CSPG including lecticans, which are found mainly in the central nervous system (CNS) of vertebrates. In vitro studies have shown a negative effect of these proteoglycans on axonal growth, mediated by depolymerization of actin filaments in the neuronal cytoskeleton. In some neurodegenerative diseases, and especially after traumatic injuries of adult CNS, there are increased levels of CSPG expression. Axonal growth inhibition by CSPG has been observed also in vivo, and therefore a strategy aimed to counteract the inhibition of axonal growth might lead to new therapies designed to restore neural circuits. There is compelling in vivo evidence that CSPG degradation by Chondroitinase ABC allows both axonal growth and functional recovery in models of injury in the mammalian CNS. These data suggest that manipulation of the response to damage could result in effective ways to promote recovery of nerve functions in neurological disorders that affect humans, such as spinal cord lesions or Parkinson disease.

Reduced expression of MAb6B4 epitopes on chondroitin sulfate proteoglycan aggrecan in perineuronal nets from cerebral cortices of SAMP10 mice: a model for age-dependent neurodegeneration

The accelerated senescence-prone SAMP10 mouse strain is a model for age-dependent neurodegeneration and is characterized by brain atrophy and deficits in learning and memory. Because perineuronal nets play an important role in the synaptic plasticity of adult brains, we examined the distributions of molecules that constitute perineuronal nets in SAMP10 mouse brain samples and compared them with those in control SAMR1 mouse samples. Proteoglycan-related monoclonal antibody 6B4 (MAb6B4) clearly immunostained perineuronal nets in SAMR1 mice cortices, but the corresponding immunostaining in SAMP10 mice was very faint. MAb6B4 recognizes phosphacan/PTPzeta in immature brains. However, this antibody recognized several protein bands, including a 400-kDa core glycoprotein from chondroitin sulfate proteoglycan in homogenates of mature cortices from SAMR1 mice. The 400-kDa band was also recognized by antiaggrecan antibodies. The aggrecan core glycoprotein band was also detectable in samples from SAMP10 mice, but this glycoprotein was faintly immunostained by MAb6B4. Because MAb6B4 recognized the same set of protein bands that the monoclonal antibody Cat-315 recognized in mature cerebral cortices of SAMR1 mice, the MAb6B4 epitope appears to be closely related to that of Cat-315 and presumably represents a novel type of oligosaccharide that attaches to aggrecans. The Cat-315 epitope colocalized with aggrecan in perineuronal nets from SAMR1 mouse brain samples, whereas its expression was prominently reduced in SAMP10 mouse brain samples. The biological significance of the MAb6B4/Cat-315 epitope in brain function and its relationship to the neurodegeneration and learning disabilities observed in SAMP10 mice remain to be elucidated.

Congenital joint dislocations caused by carbohydrate sulfotransferase 3 deficiency in recessive Larsen syndrome and humero-spinal dysostosis

Deficiency of carbohydrate sulfotransferase 3 (CHST3; also known as chondroitin-6-sulfotransferase) has been reported in a single kindred so far and in association with a phenotype of severe chondrodysplasia with progressive spinal involvement. We report eight CHST3 mutations in six unrelated individuals who presented at birth with congenital joint dislocations. These patients had been given a diagnosis of either Larsen syndrome (three individuals) or humero-spinal dysostosis (three individuals), and their clinical features included congenital dislocation of the knees, elbow joint dysplasia with subluxation and limited extension, hip dysplasia or dislocation, clubfoot, short stature, and kyphoscoliosis developing in late childhood. Analysis of chondroitin sulfate proteoglycans in dermal fibroblasts showed markedly decreased 6-O-sulfation but enhanced 4-O-sulfation, confirming functional impairment of CHST3 and distinguishing them from diastrophic dysplasia sulphate transporter (DTDST)-deficient cells. These observations provide a molecular basis for recessive Larsen syndrome and indicate that recessive Larsen syndrome, humero-spinal dysostosis, and spondyloepiphyseal dysplasia Omani type form a phenotypic spectrum.

Cartilage is held together by elastic glycan strings. Physiological and pathological implications

Animal shapes are maintained by connective tissue extracellular matrices (ECMs). ECM shapes depend on keeping collagen fibrils in the right places, held by regular frequent proteoglycan (PG) bridges attached at specific sites. The PGs carry anionic glycosaminoglycan (AGAG) 'strings' that span and determine interfibrillar distances, thus holding us together. I called these repeating structures 'shape modules'. The strings are aggregated antiparallel chains of dermochondan, keratan and chondroitan sulphates (DS, KS and CS); stabilised by hydrophobic and H-bonds. Shape modules are elastic. AGAG/AGAG interactions break under stress and reform when the stress is removed and/or they contain an elastic sugar, L-iduronate (in DS). Cartilage ECMs are also based on shape modules. Depots therein of aggrecan, the large PG which carries many chains of CS and KS, imbibe water, thereby exerting swelling pressure. External pressure forces this water into the elastic shape modules, from whence it is returned post compression. Cartilage anisotropic responses (along and at right angles to shape module axes) to compressive and tensile stresses are now interpretable. Degradation of shape modules in osteoarthrosis reduces these responses. Inability to hold collagen fibrils together results in imbibition of excess water, fissuring and erosion, characteristic of this condition.

Fibromodulin binds collagen type I via Glu-353 and Lys-355 in leucine-rich repeat 11

Fibromodulin belongs to the small leucine-rich repeat proteoglycan family, interacts with collagen type I, and controls collagen fibrillogenesis and assembly. Here, we show that a major fibromodulin-binding site for collagen type I is located in leucine-rich repeat 11 in the C terminus of the leucine-rich repeat domain. We identified Glu-353 and Lys-355 in repeat 11 as essential for binding, and the synthetic peptide RLDGNEIKR, including Glu-353 and Lys-355, inhibits the binding of fibromodulin to collagen in vitro. Fibromodulin and lumican compete for the same binding region on collagen, and fibromodulin can inhibit the binding of lumican to collagen type I. However, the peptide RLDGNEIKR does not inhibit the binding of lumican to collagen, suggesting separate but closely situated fibromodulin- and lumican-binding sites in collagen. The collagen-binding Glu-353 and Lys-355 residues in fibromodulin are exposed on the exterior of the beta-sheet-loop structure of the leucine-rich repeat, which resembles the location of interacting residues in other leucine-rich repeat proteins, e.g. decorin.

The role of chondroitin sulfate proteoglycans in regeneration and plasticity in the central nervous system

Chondroitin sulfate proteoglycans (CSPGs) consist of a core protein and glycosaminoglycan (GAG) chains. There is enormous structural diversity among CSPGs due to variation in the core protein, the number of GAG chains and the extent and position of sulfation. Most CSPGs are secreted from cells and participate in the formation of the extracellular matrix (ECM). CSPGs are able to interact with various growth-active molecules and this may be important in their mechanism of action. In the normal central nervous system (CNS), CSPGs have a role in development and plasticity during postnatal development and in the adult. Plasticity is greatest in the young, especially during critical periods. CSPGs are crucial components of perineuronal nets (PNNs). PNNs have a role in closure of the critical period and digestion of PNNs allows their re-opening. In the adult, CSPGs play a part in learning and memory and the hypothalamo-neurohypophysial system. CSPGs have an important role in CNS injuries and diseases. After CNS injury, CSPGs are the major inhibitory component of the glial scar. Removal of CSPGs improves axonal regeneration and functional recovery. CSPGs may also be involved in the pathological processes in diseases such as epilepsy, stroke and Alzheimer's disease. Several possible methods of manipulating CSPGs in the CNS have recently been identified. The development of methods to remove CSPGs has considerable therapeutic potential in a number of CNS disorders.

Lumican, a small leucine-rich proteoglycan substituted with keratan sulfate chains is expressed and secreted by human melanoma cells and not normal melanocytes

Melanoma is a frequent and therapy-resistant human disease. Malignant melanocytes modulate their microenvironment in order to penetrate the dermal/epidermal junction and eventually invade the dermis. The small leucine-rich proteoglycans (SLRPs) constitute important constituents of the dermis extracellular matrix (ECM), participating in both the structural and the functional organization of the skin. The role of a keratan sulphate SLRP lumican, has recently been investigated in the growth and metastasis of several cancers. In this study, the expression of lumican was studied in two human melanoma cell lines (WM9, M5) as well as in normal neonatal human melanocytes (HEMN) using real time PCR, western blotting with antibodies against the protein core and keratan sulfate, and treatments with specific enzymes. Both human metastatic melanoma cell lines were found to express lumican mRNA and effectively secrete lumican in a proteoglycan form, characterized to be substituted mostly with keratan sulfate chains. Lumican mRNA was not detected in normal melanocytes. This is the first time that the synthesis and secretion of lumican in human melanoma cell lines is reported. The role of this proteoglycan in the development and progression of malignant melanoma has to be further investigated.

Chondroitin sulphate proteoglycans in the vitreous gel of sheep and goat

In the present study, the amounts and the fine structural characteristics of chondroitin sulphate proteoglycans (CSPGs) present in sheep and goat vitreous gels were determined. The results showed that in both examined species hyaluronan was the predominant glycosaminoglycan (GAG), whereas CSPGs were present in minor amounts. CSPGs were identified as versican and collagen IX with versican being the predominant PG type. Fine structural characterization indicated that the CS chains of versican in both mammalian species were of smaller size than those found in collagen IX. The difference in the sulphation pattern of CS chains between versican and collagen IX was also of particular interest. The results indicated that the predominant disaccharide type in CS side chains of versican and collagen IX from both sheep and goat vitreous gels was the 4-sulphated disaccharide. CS chains of versican were found to be richer in 4-sulphated disaccharide units than those in collagen IX, which also contained a significant proportion of non-sulphated disaccharides. These findings showed that, firstly, the CS content and the hydrodynamic size of the CS chain and, secondly, the sulphation pattern of CS chains from versican and collagen IX in both sheep and goat vitreous gels are PG type-dependent.

Development of an apparatus for rapid release of oligosaccharides at the glycosaminoglycan-protein linkage region in chondroitin sulfate-type proteoglycans

An apparatus, AutoGlycoCutter (AGC), was developed as a tool for rapid release of O-linked-type glycans under alkaline conditions. This system allowed rapid release of oligosaccharides at the glycosaminoglycan-protein linkage region in proteoglycans (PGs). After digestion of PGs with chondroitinase ABC, the oligosaccharides at the linkage region were successfully released from the protein core by AGC within 3 min. The reducing ends of the released oligosaccharides were labeled with 2-aminobenzoic acid and analyzed by a combination of capillary electrophoresis (CE) and matrix-assisted laser desorption time-of-flight mass spectrometry. In addition, the unsaturated disaccharides produced by chondroitinase ABC derived from the outer parts of the glycans were labeled with 2-aminoacridone and analyzed by CE to determine the disaccharide compositions. We evaluated AGC as a method for structural analysis of glycosaminoglycans in some chondroitin-sulfate-type PGs (urinary trypsin inhibitor, bovine nasal cartilage PG, bovine aggrecan, bovine decorin, and bovine biglycan). Recoveries of the released oligosaccharides were 57-73% for all PGs tested in the present study. In particular, we emphasize that the use of AGC achieved ca. 1000-fold rapid release of O-glycans compared with the conventional method.

Force-mediated dissociation of proteoglycan aggregate in articular cartilage

Proteoglycan aggregate is the primary component in articular cartilage responsible for resisting compressive loading. It consists of a core molecule of hyaluronan and a number of side chains of aggrecan bound to hyaluronan non-covalently. The loss of aggrecan from articular cartilage is considered to be a major factor in the development of osteoarthritis. Though enzymatic digestion of aggrecan is believed to be responsible for the release of aggrecan from osteoarthritic cartilage, other mechanisms, such as direct force-mediated detachment of aggrecan from hyaluronan may also be involved. In this study, the rupture force of the single bond between hyaluronan and aggrecan in articular cartilage was directly quantified using experimental measurement and Monte Carlo simulation. Low rupture force of this bond, as determined in this study suggested a possible direct force-mediated detachment of aggrecan from proteoglycan aggregate in osteoarthritic cartilage.

Neuroglycan C Is a Novel Midkine Receptor Involved in Process Elongation of Oligodendroglial Precursor-like Cells

Midkine is a heparin-binding growth factor that promotes cell attachment and process extension in undifferentiated bipolar CG-4 cells, an oligodendroglial precursor cell line. We found that CG-4 cells expressed a non-proteoglycan form of neuroglycan C, known as a part-time transmembrane proteoglycan. We demonstrated that neuroglycan C before or after chondroitinase ABC treatment bound to a midkine affinity column. Neuroglycan C lacking chondroitin sulfate chains was eluted with 0.5 m NaCl as a major fraction from the column. We confirmed that CG-4 cells expressed two isoforms of neuroglycan C, I, and III, by isolating cDNA. Among three functional domains of the extracellular part of neuroglycan C, the chondroitin sulfate attachment domain and acidic amino acid cluster box domain showed affinity for midkine, but the epidermal growth factor domain did not. Furthermore, cell surface neuroglycan C could be cross-linked with soluble midkine. Process extension on midkine-coated dishes was inhibited by either a monoclonal anti-neuroglycan C antibody C1 or a glutathione S-transferase-neuroglycan C fusion protein. Finally, stable transfectants of B104 neuroblastoma cells overexpressing neuroglycan C-I or neuroglycan C-III attached to the midkine substrate, spread well, and gave rise to cytoskeletal changes. Based on these results, we conclude that neuroglycan C is a novel component of midkine receptors involved in process elongation.

Crystal Structure of Unsaturated Glucuronyl Hydrolase Complexed with Substrate

Unsaturated glucuronyl hydrolase (UGL), which is a member of glycoside hydrolase family GH-88, is a bacterial enzyme that degrades mammalian glycosaminoglycans and bacterial biofilms. The enzyme, which acts on unsaturated oligosaccharides with an alpha-glycoside bond produced by microbial polysaccharide lyases responsible for bacterial invasion of host cells, was believed to release 4-deoxy-l-threo-5-hexosulose-uronate (unsaturated glucuronic acid, or DeltaGlcA) and saccharide with a new nonreducing terminus by hydrolyzing the glycosidic bond. We detail the crystal structures of wild-type inactive mutant UGL of Bacillus sp. GL1 and its complex with a substrate (unsaturated chondroitin disaccharide), identify active site residues, and postulate a reaction mechanism catalyzed by UGL that triggers the hydration of the vinyl ether group in DeltaGlcA, based on the structural analysis of the enzyme-substrate complex and biochemical analysis. The proposed catalytic mechanism of UGL is a novel case among known glycosidases. Under the proposed mechanism, Asp-149 acts as a general acid and base catalyst to protonate the DeltaGlcA C4 atom and to deprotonate the water molecule. The deprotonated water molecule attacks the DeltaGlcA C5 atom to yield unstable hemiketal; this is followed by spontaneous conversion to an aldehyde (4-deoxy-l-threo-5-hexosulose-uronate) and saccharide through hemiacetal formation and cleavage of the glycosidic bond. UGL is the first clarified alpha(6)/alpha(6)-barrel enzyme using aspartic acid as the general acid/base catalyst.

SLRP interaction can protect collagen fibrils from cleavage by collagenases

Decorin, fibromodulin and lumican are small leucine-rich repeat proteoglycans (SLRPs) which interact with the surface of collagen fibrils. Together with other molecules they form a coat on the fibril surface which could impede the access to collagenolytic proteinases. To address this hypothesis, fibrils of type I or type II collagen were formed in vitro and treated with either collagenase-1 (MMP1) or collagenase-3 (MMP13). The fibrils were either treated directly or following incubation in the presence of the recombinant SLRPs. The susceptibility of the uncoated and SLRP-coated fibrils to collagenase cleavage was assessed by SDS/PAGE. Interaction with either recombinant decorin, fibromodulin or lumican results in decreased collagenase cleavage of both fibril types. Thus SLRP interaction can help protect collagen fibrils from cleavage by collagenases.

Solution structure and dynamics of cartilage aggrecan

We studied the structure and dynamics of porcine laryngeal aggrecan in solution using a range of noninvasive techniques: dynamic light scattering (DLS), small-angle neutron scattering (SANS), video particle tracking (VPT) microrheology, and diffusing wave spectroscopy (DWS). The data are analyzed within the framework of a combined static and dynamic scaling model, and evidence is found for reptation of the comb backbones with unentangled side-chain dynamics. Small-angle neutron scattering indicated standard polyelectrolyte scaling of the mesh size (xi) with concentration (c) in semidilute solutions for the whole aggrecan aggregate, xi = Ac(-0.47+/-0.04), with the prefactor (A) implying there is on average 60 nm between the aggrecan subunits along the backbone. VPT demonstrated large exponents for the power law dependence of the intrinsic viscosity (eta) on the polymer concentration in the semidilute concentration regime, eta approximately c(alpha); with alpha equal to 2.04 +/- 0.06 and 1.95 +/- 0.08 for the assembled and disassembled aggrecan aggregates, respectively. DWS at high frequencies (10(4)-10(5) Hz) gave evidence for internal Rouse modes of the aggrecan monomers, independent of the degree of self-assembly of the molecules.

Monoclonal antibody Cat-315 detects a glycoform of receptor protein tyrosine phosphatase beta/phosphacan early in CNS development that localizes to extrasynaptic sites prior to synapse formation

Perineuronal nets (PNs) are lattice-like condensations of the extracellular matrix (ECM) that envelop synapses and decorate the surface of subsets of neurons in the CNS. Previous work has suggested that, despite the fact that PNs themselves are not visualized until later in development, some PN component molecules are expressed in the rodent CNS even before synaptogenesis. In the adult mammalian brain, monoclonal antibody Cat-315 recognizes a glycoform of aggrecan, a major component of PNs. In primary cortical cultures, a Cat-315-reactive chondroitin sulfate proteoglycan (CSPG) is also expressed on neuronal surfaces and is secreted into culture media as early as 24 h after plating. In this study, we show that in primary cortical cultures, the Cat-315 CSPG detected in early neural development is expressed in extrasynaptic sites prior to synapse formation. This suggests that ECM components in the CNS, as in the neuromuscular junction (NMJ), may prepattern neuronal surfaces prior to innervation. We further show that while the Cat-315-reactive carbohydrate decorates aggrecan in the adult, it decorates a different CSPG in the developing CNS. Using receptor protein tyrosine phosphatase beta (RPTPbeta/protein tyrosine phosphatase zeta) knock-out mice and immunoprecipitation techniques, we demonstrate here that in the developing rodent brain Cat-315 recognizes RPTPbeta isoforms. Our further examination of the Cat-315 epitope suggests that it is an O-mannose linked epitope in the HNK-1 family. The presence of the Cat-315 reactive carbohydrate on different PN components--RPTPbeta and aggrecan--at different stages of synapse development suggests a potential role for this neuron-specific carbohydrate motif in synaptogenesis.

Cartilage aggrecan undergoes significant compositional and structural alterations during laryngeal cancer

Aggrecan is a key component of cartilage and is responsible for the integrity and function of the tissue. In this study, the content of aggrecan and its structural modifications in adjacent to cancer apparently normal cartilages (AANCs) from various stages of laryngeal squamous cell carcinoma (LSCC) were investigated. Our data demonstrated a stage-related loss of aggregable aggrecan in AANCs, compared to the healthy laryngeal cartilage (HLC), which was excessive in advanced stages of disease. On aggregable aggrecan level, AANCs were characterized by significant compositional and structural modifications, the extent of which was closely related with the stage of LSCC. Four concrete subpopulations of aggregable molecules with particular physicochemical characteristics were identified with a strong tendency to prevail subpopulations of molecules of lower hydrodynamic sizes with increasing LSCC stage. These findings demonstrated that the cleavage of aggregable aggrecan occurred in concrete peptide bonds within the CS-1 and CS-2 attachment domains. These significant alterations were closely associated with the process of cartilage destruction, indicating the crucial role of aggrecan during LSCC.

Identification of novel chondroitin proteoglycans in Caenorhabditis elegans: embryonic cell division depends on CPG-1 and CPG-2

Vertebrates produce multiple chondroitin sulfate proteoglycans that play important roles in development and tissue mechanics. In the nematode Caenorhabditis elegans, the chondroitin chains lack sulfate but nevertheless play essential roles in embryonic development and vulval morphogenesis. However, assignment of these functions to specific proteoglycans has been limited by the lack of identified core proteins. We used a combination of biochemical purification, Western blotting, and mass spectrometry to identify nine C. elegans chondroitin proteoglycan core proteins, none of which have homologues in vertebrates or other invertebrates such as Drosophila melanogaster or Hydra vulgaris. CPG-1/CEJ-1 and CPG-2 are expressed during embryonic development and bind chitin, suggesting a structural role in the egg. RNA interference (RNAi) depletion of individual CPGs had no effect on embryonic viability, but simultaneous depletion of CPG-1/CEJ-1 and CPG-2 resulted in multinucleated single-cell embryos. This embryonic lethality phenocopies RNAi depletion of the SQV-5 chondroitin synthase, suggesting that chondroitin chains on these two proteoglycans are required for cytokinesis.

The glycosaminoglycan attachment regions of human aggrecan

Aggrecan possesses both chondroitin sulfate (CS) and keratan sulfate (KS) chains attached to its core protein, which reside mainly in the central region of the molecule termed the glycosaminoglycan-attachment region. This region is further subdivided into the KS-rich domain and two adjacent CS-rich domains (CS1 and CS2). The CS1 domain of the human is unique in exhibiting length polymorphism due to a variable number of tandem amino acid repeats. The focus of this work was to determine how length polymorphism affects the structure of the CS1 domain and whether CS and KS chains can coexist in the different glycosaminoglycan-attachment domains. The CS1 domain possesses several amino acid repeat sequences that divide it into three subdomains. Variation in repeat number may occur in any of these domains, with the consequence that CS1 domains of the same length may possess different amino acid sequences. There was no evidence to support the presence of KS in either the CS1 or the CS2 domains nor the presence of CS in the KS-rich domain. The structure of the CS chains was shown to vary between the CS1 and CS2 domains, particularly in the adult, with variation occurring in chain length and the sulfation of the non-reducing terminal N-acetyl galactosamine residue. CS chains in the adult CS2 domain were shorter than those in the CS1 domain and possessed disulfated terminal residues in addition to monosulfated residues. There was, however, no change in the sulfation pattern of the disaccharide repeats in the CS chains from the two domains.

Versican G3 domain regulates neurite growth and synaptic transmission of hippocampal neurons by activation of epidermal growth factor receptor

Versican is one of the major extracellular matrix (ECM) proteins in the brain. ECM molecules and their cleavage products critically regulate the growth and arborization of neurites, hence adjusting the formation of neural networks. Recent findings have revealed that peptide fragments containing the versican C terminus (G3 domain) are present in human brain astrocytoma. The present study demonstrated that a versican G3 domain enhanced cell attachment, neurite growth, and glutamate receptor-mediated currents in cultured embryonic hippocampal neurons. In addition, the G3 domain intensified dendritic spines, increased the clustering of both synaptophysin and the glutamate receptor subunit GluR2, and augmented excitatory synaptic activity. In contrast, a mutated G3 domain lacking the epidermal growth factor (EGF)-like repeats (G3deltaEGF) had little effect on neurite growth and glutamatergic function. Treating the neurons with the G3-conditioned medium rapidly increased the levels of phosphorylated EGF receptor (pEGFR) and phosphorylated extracellular signal-regulated kinase (pERK), indicating an activation of EGFR-mediated signaling pathways. Blockade of EGFR prevented the G3-induced ERK activation and suppressed the G3-provoked enhancement of neurite growth and glutamatergic function but failed to block the G3-mediated enhancement of cell attachment. These combined results indicate that the versican G3 domain regulates neuronal attachment, neurite outgrowth, and synaptic function of hippocampal neurons via EGFR-dependent and -independent signaling pathway(s). Our findings suggest a role for ECM proteolytic products in neural development and regeneration.

Glycoform quantification of chondroitin/dermatan sulfate using a liquid chromatography-tandem mass spectrometry platform

Chondroitin sulfate (CS) is a glycosaminoglycan consisting of repeating uronic acid, N-acetylgalactosamine disaccharide units {[HexAbeta/alpha(1-3)GalNAcbeta(1-4)](n)()}. CS chains are polydisperse with respect to chain length, sulfate content, and glucuronic acid epimerization content, resulting in a distribution of glycoforms for a chain bound to any given serine residue. Usually, CS glycoforms exist, differing in sulfation position and uronic acid epimerization. This work introduces a novel LC-MS/MS platform for the quantification of mixtures of CS oligosaccharides. The CS polysaccharides were partially depolymerized and labeled with either the light (d(0)) or heavy (d(4)) form of 2-anthranilic acid (2-AA). Excess reagent was removed, and mixtures of the CS standard (d(0)) and unknown (d(4)) were made. The CS mixture was subjected to size exclusion chromatography (SEC) with on-line electrospray ionization mass spectrometric detection in the negative ion mode. Tandem mass spectra were acquired, and quantification of unknown samples within the mixture was made using relative ion abundances of specific diagnostic ions. The high accuracy and precision of the glycomics platform were demonstrated using glycoform mixtures made from standard CS preparations. The CS glycoform analysis method was then applied to cartilage extract, versican, and several dermatan sulfate preparations. This work presents the first application of a glycomics platform for the quantification of CS oligosaccharide mixtures for obtaining specific information about the positions of GalNAc sulfation and uronic acid epimerization.

Molecular Evolution and Functionally Important Structures of Molluscan Dermatopontin: Implications for the Origins of Molluscan Shell Matrix Proteins

A major shell matrix protein originally obtained from a freshwater snail is a molluscan homologue of Dermatopontins, a group of Metazoan proteins also called TRAMP (tyrosine-rich acidic matrix protein). We sequenced and identified 14 molluscan homologues of Dermatopontin from eight snail species belonging to the order Basommatophora and Stylommatophora. The bassommatophoran Dermatopontins fell into three types, one is suggested to be a shell matrix protein and the others are proteins having more general functions based on gene expression analyses. N-glycosylation is inferred to be important for the function involved in shell calcification, because potential N-glycosylation sites were found exclusively in the Dermatopontins considered as shell matrix proteins. The stylommatophoran Dermatopontins fell into two types, also suggested to comprise a shell matrix protein and a protein having a more general function. Phylogenetic analyses using maximum likelihood and Bayesian methods revealed that gene duplication events occurred independently in both basommatophoran and stylommatophoran lineages. These results suggest that the dermatopontin genes were co-opted for molluscan calcification at least twice independently after the divergence of basommatophoran and stylommatophoran lineages, or more recently than we have expected.

Repulsive guidance of axons of spinal sensory neurons in Xenopus laevis embryos: roles of Contactin and notochord-derived chondroitin sulfate proteoglycans

An immunoglobulin superfamily neuronal adhesion molecule, Contactin, has been implicated in axon guidance of spinal sensory neurons in Xenopus embryos. To identify the guidance signaling molecules that Contactin recognizes in tailbud embryos, an in situ binding assay was performed using recombinant Contactin-alkaline phosphatase fusion protein (Contactin-AP) as a probe. In the assay of whole-mount or sectioned embryos, Contactin-AP specifically bound to the notochord and its proximal regions. This binding was completely blocked by either digestion of embryo sections with chondroitinase ABC or pretreatment of Contactin-AP with chondroitin sulfate A. When the spinal cord and the notochord explants were co-cultured in collagen gel, growing Contactin-positive spinal axons were repelled by notochord-derived repulsive activity. This repulsive activity was abolished by the addition of either a monoclonal anti-Contactin antibody, chondroitin sulfate A or chondroitinase ABC to the culture medium. An antibody that recognizes chondroitin sulfate A and C labeled immunohistochemically the notochord in embryo sections and the collagen gel matrix around the cultured notochord explant. Addition of chondroitinase ABC into the culture eliminated the immunoreactivity in the gel matrix. These results suggest that the notochord-derived chondroitin sulfate proteoglycan acts as a repulsive signaling molecule that is recognized by Contactin on spinal sensory axons.

Versican G3 domain promotes blood coagulation through suppressing the activity of tissue factor pathway inhibitor-1

We have detected versican, a member of the large chondroitin sulfate proteoglycans, and its degraded C-terminal G3 fragments in human plasma and observed that the versican G3 domain promoted blood coagulation. Silencing G3 expression with small interfering RNA reduced the effect of G3 on coagulation. Plasma coagulation assays suggest that G3 enhances coagulation irrespective of its actions on platelets and white blood cells. To examine how versican affected blood coagulation, we used normal human plasma and different types of coagulation factor-deficient plasmas. The experiments indicated that versican enhanced coagulation through the extrinsic pathway, and that Factor VII was the target molecule. FVII activity assays showed that G3 activated FVII in the presence of plasma but not with purified FVII directly. Yeast two-hybrid, immunoprecipitation, and gel co-migration assays showed that G3 interacted with the tissue factor pathway inhibitor-1 (TFPI-1). TFPI-1 activity assays suggested that G3 inhibited TFPI-1 activity, allowing FVIIa and FXa to facilitate the coagulation process. G3-induced blood coagulation was further confirmed with a mouse model in a real-time manner. Taken together, these results indicate that versican may represent a new target for the development of therapies against atherosclerosis.

The involvement of aggrecan polymorphism in degeneration of human intervertebral disc and articular cartilage

The functions of the intervertebral disc and of articular cartilage are intimately related to their aggrecan content. Aggrecan is a proteoglycan that interacts with hyaluronan to form large aggregates, which are responsible for the ability of the tissues to resist compressive loads. This function is related to the structure of aggrecan, and in particular to the large number of chondroitin sulphate chains present on its core protein. The chondroitin sulphate chains are present in two adjacent regions of the aggrecan core protein, termed the CS1 and CS2 domains. In the human, the region of the aggrecan gene encoding the CS1 domain exhibits size polymorphism, which can result in variation in the degree of chondroitin sulphate substitution of aggrecan in different individuals. This raises the possibility that the functional properties of aggrecan may vary between individuals, and that those individuals with an inferior aggrecan structure may be more susceptible to premature intervertebral disc or articular cartilage degeneration. Several studies have been performed to demonstrate such an association, but the results have been ambiguous. This review explains the relationship between aggrecan structure and function, describes the technique used to assess aggrecan polymorphism and the conclusions and limitations of the data obtained to date, and discusses the implications for tissue degeneration and clinical practice.

A sulfated disaccharide derived from chondroitin sulfate proteoglycan protects against inflammation-associated neurodegeneration

Chondroitin sulfate proteoglycan (CSPG), a matrix protein that occurs naturally in the central nervous system (CNS), is considered to be a major inhibitor of axonal regeneration and is known to participate in activation of the inflammatory response. The degradation of CSPG by a specific enzyme, chondroitinase ABC, promotes repair. We postulated that a disaccharidic degradation product of this glycoprotein (CSPG-DS), generated following such degradation, participates in the modulation of the inflammatory responses and can, therefore, promote recovery in immune-induced neuropathologies of the CNS, such as experimental autoimmune encephalomyelitis (EAE) and experimental autoimmune uveitis (EAU). In these pathologies, the dramatic increase in T cells infiltrating the CNS is far in excess of the numbers needed for regular maintenance. Here, we show that CSPG-DS markedly alleviated the clinical symptoms of EAE and protected against the neuronal loss in EAU. The last effect was associated with a reduction in the numbers of infiltrating T cells and marked microglia activation. This is further supported by our in vitro results indicating that CSPG-DS attenuated T cell motility and decreased secretion of the cytokines interferon-gamma and tumor necrosis factor-alpha. Mechanistically, these effects are associated with an increase in SOCS-3 levels and a decrease in NF-kappaB. Our results point to a potential therapeutic modality, in which a compound derived from an endogenous CNS-resident molecule, known for its destructive role in CNS recovery, might be helpful in overcoming inflammation-induced neurodegenerative conditions.

Dermatopontin, a novel player in the biology of the extracellular matrix

Dermatopontin is a widely distributed small molecular weight protein in the extracellular matrix (ECM) and today its homologues are known in five mammals and several invertebrates. The structures of these homologues are relatively well conserved among the species. In the skin, dermatopontin is located mainly on the surface of the collagen fibers. It is found in the conditioned medium and also in the cytoplasm of cultured fibroblasts. Early studies focused on ECM assembly (collagen fibrillogenesis) and interactions (with the proteoglycan decorin). Subsequently, a targeted disruption of dermatopontin resulted in a phenotype similar to Ehlers-Danlos syndrome. In addition, a cell adhesion activity of this protein for dermal fibroblasts and several other cells was found, and this activity might suggest this protein's involvement in wound healing. The expression of dermatopontin around an infarct zone of experimental myocardial infarction may support this possibility. In invertebrates, dermatopontin homologues act mainly as adhesion/agglutination molecules. In addition, we found that transforming growth factor-beta1 interacts with dermatopontin and the function of this cytokine is modified by dermatopontin. Recently, the involvement of this protein in cell proliferation has been indicated. In this review we describe the reported functions of this protein and speculate on the multiple roles of this largely uncharacterized matrix molecule.

Versican: signaling to transcriptional control pathways

Versican, a chondroitin sulfate proteoglycan, is one of the main components of the extracellular matrix, which provides a loose and hydrated matrix during key events in development and disease. Versican participates in cell adhesion, proliferation, migration, and angiogenesis, and hence plays a central role in tissue morphogenesis and maintenance. In addition, versican contributes to the development of a number of pathologic processes including atherosclerotic vascular diseases, cancer, tendon remodeling, hair follicle cycling, central nervous system injury, and neurite outgrowth. Versican is a complex molecule consisting of modular core protein domains and glycosaminoglycan side chains, and there are various steps of synthesis and processes regulating them. Also, there is differential temporal and spatial expression of versican by multiple cell types and in different developmental and pathological time frames. To fully appreciate the functional roles of versican as it relates to changing patterns of expression in development and disease, an in depth knowledge of versican's biosynthetic processing is necessary. The goal of this review is to evaluate the current status of our knowledge regarding the transcriptional control of versican gene regulation. We will be focusing on the signal transduction pathways, promoter regions, cis-acting elements, and trans-factors that have been characterized.